When to Epoxy

My thanks to all of you who rplied to my question about joints, now for the next question.

I have designs for a San Javior Kayak (I think they are out of business now, not sure), this is a Stich & Glue kayak. How much of the epoxying can be done before actually stiching the pieces together? can I put fibreglass tape and epoxy over pieces that have already had a coat of put on them? I would prefer to do most of my epoxy work on a flat working surface if I can get away with it.

 

My first thought is to follow the designers instructions.
Briany

 

Adhesion and bond strength is much greater for a "primary" as opposed to a "secondary" bond in wood/epoxy construction. The further along the cure is on the underlying epoxy layer, the more the bond relies on mechanical keying (sanded or scuffed surfaces) as opposed to a chemical bond.

Cured epoxy often has a kind of greasy film called amine blush that should be removed by scrubbing with a Scotchbrite pad or wet and dry sandpaper and clean, warm water. Dry thoroughly. You may still need further scuff sanding at areas that are going to carry structural loads, such as where you're tabbing in a bulkhead to a hull side. Careful not to saturate adajacent raw wood or you'll be waiting a long time for it to dry before you can re-coat.

For a stitch and glue kayak, stich it together with thin nylon cable ties. Wetout your seams, apply the interior fillets, lay down the tape, and get the first coat over the entire raw interior in 1 shot. If that's too much, at least get the seams filleted and taped to raw plywood. The only place I'd even think about precoating a surface and letting it cure before installation on a kayak would be the underside of the deck panels. I'd be inclined to mask the areas that will be bonded to gunwales or deckbeams to keep them epoxy free and glue those up just before I fastened the deck down.

Besides the weaker, secondary bond you'll get using pre-coated, cured panels, the panels will also be stiffer, possibly to the point of not bending into the desired shape without a fight.

 

I would sugest you read some of the "Epoxy Works" from Gougeon Brothers. A More lengthy read would be their "The Gougeon Brothers On Boat Construction"
A neat trick from Epoxy Works, was to put a dowel under the wire ties, on the inside of the joint, thus centering the joint of the two panels, then apply the tape between the dowels. Once the epoxy had cured and the ties and dowels removed the joints were finished with tape and filler.

 

I wish to read some of the epoxy works from Gougeon Brothers.

 

does epoxy better to use in manufacturing fiberglass external doors?

 

Epoxy can cost 4 times as much as other stuff...
- Perhaps....'caus it WORKS - 4 times better.

Studies have been done that, generaly, the
strength of a given material is suprisingly
connected to it's cost........

 

That is not true. It might be an indicator, all other things being equal, but that is about it.

Metals: Tell me that price is connected to strength.

Wood: Likewise.

It's only true in the sense that a material that is better, often cost more than the inferior, but from that you cannot deduct the other way around (i.e. that because it is dearer, thus it must be better). If you think so, I have a slew of rebranded products to sell you. I tell you, they're good. They're expensive (now, after the rebrand, you see), so they _must_ be good.

 

'Glass doors are made of polyester because the combination of materials is more then adequate for the tasks asked of it. Sure you could build a 'glass door with epoxy resin instead. You'd now be making a door much stronger and more costly then necessary and most successful business profiles, don't include this level of over manufacturing in their bottom line.

Back to the original poster's questions. It would be nice if we could work in the down hand position, all the time. Not crawling around in the narrow confines of a boat, smearing on goo would be wonderful. Yes, you can do some of your epoxy work before bending those panels in place. You could CPES the ply first and when dry, it will be quite flexible and not resist your efforts to bend the panels into alignment. Regular laminating epoxy will impart some stiffness to the panels, maybe making portions of the fitting process more trouble. You also risk the chance of cracking, splitting and other wise damaging the dried coating while you'll bend them into shape.

In all fairness, I don't think you'd save much time and effort pre-coating with anything other then a CPES type product. All the seams should be left bare, so you can have a good bond when the tape and goo goes in. On a kayak there isn't much epoxy work to perform, maybe less then 150' of seams that need to be filleted and taped, plus the sheathing. Once the seams are drawn up with ties, everything squared up good, you can epoxy up a typical single chine kayak in an easy day, sheath the next.

Some designs will permit the sheer clamp to be installed, before the panels are stitched and there are many parts that surly can be done (epoxied) before hand. The structural requirements for these hull seams account for much of the boat's strength, so good procedures need to be practiced, like wet on green lay ups, etc.

I think you'll find, the actual goo in your hand time is small, compared to the other elements of the build.